Prosthetic pylon having an enclosed compressible volume of fluid to support a patient&#39;s weight

ABSTRACT

A pylon includes a first end portion connected to a patient&#39;s leg stump and a second end portion connected to a prosthetic foot. The second end portion includes a piston, and the first end portion includes a piston chamber receiving the piston. The second end portion is thus rotatable and axially movable relative to the first end portion about and along a longitudinal axis of the pylon, respectively. The piston chamber encloses a compressible volume of fluid through which substantially all of the patient&#39;s weight applied through the patient&#39;s leg stump is supported. The compressible volume of fluid is sealed so that it can be pressurized. Also, a torsional spring couples the piston and piston chamber and resists relative rotation between the piston and piston chamber without supporting any substantial portion of the patient&#39;s weight applied through the patient&#39;s leg stump to the piston. The present invention thus advantageously provides a pylon which is more cushioned and resilient than conventional pylons.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent application Ser. No. 09/442,255, filed Nov. 17, 1999, which is a continuation of U.S. patent application Ser. No. 08/939,134, filed Sep. 29, 1997, now U.S. Pat. No. 6,086,615, which is a continuation of U.S. patent application Ser. No. 08/527,514, filed Sep. 12, 1995, now U.S. Pat. No. 5,702,488.

TECHNICAL FIELD

[0002] The present invention relates in general to a prosthetic pylon, and in particular to a prosthetic pylon supporting the weight of a patient on a compressible volume of fluid.

BACKGROUND OF THE INVENTION

[0003] Individuals who lose all or part of a leg have a residual leg stump to which a prosthetic foot is often attached through an elongated pylon. Such a pylon is typically a rigid member made with a material, like a carbon-fiber composite or aluminum, which provides the rigidity necessary to support an individual's weight.

[0004] This rigidity can be problematic, because it often makes conventional pylons too stiff for comfortable movement. Each step on such a pylon can be awkward and painful, rather than cushioned and resilient like a natural leg. Therefore, there is a need in the art for a pylon which adequately supports an individual's weight and is more cushioned and resilient than conventional pylons.

SUMMARY OF THE INVENTION

[0005] A pylon constructed in accordance with one embodiment of the invention includes a first end portion connected to a patient's leg stump and a second end portion connected to a prosthetic foot. The second end portion is rotatable and axially movable relative to the first end portion about and along a longitudinal axis of the pylon, respectively. Preferably, the second end portion includes a piston, and the first end portion includes a piston chamber receiving the piston. The piston chamber encloses a compressible volume of fluid through which substantially all of the patient's weight applied through the patient's leg stump is supported. The compressible volume of fluid is preferably sealed so that it can be pressurized. Also, a torsional spring couples the piston and piston chamber and resists relative rotation between the piston and piston chamber without supporting any substantial portion of the patient's weight applied through the patient's leg stump. The present invention thus provides a pylon which is more cushioned and resilient than conventional pylons.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is an isometric view of a prosthetic system using the inventive pylon.

[0007]FIG. 2 is a side cross-sectional view of the inventive pylon of FIG. 1.

[0008]FIG. 3 is a plan cross-sectional view of a torsional spring of the inventive pylon of FIG. 1.

[0009]FIG. 4 is a side cross-sectional view of a pylon having a membrane in accordance with an embodiment of the invention.

[0010]FIG. 5 is a side cross-sectional view of a pylon having a bladder in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] With reference to FIG. 1, one embodiment of the present invention provides a prosthetic system 10 comprising a prosthetic foot 12 and a pylon 14. The pylon 14 has a first end portion 16 releasably connected to a conventional socket 18 into which a patient's leg stump fits, and a second end portion 20 releasably connected to the prosthetic foot 12. The second end portion 20 is rotatable relative to the first end portion 16 about a longitudinal axis 22 of the pylon 14, and is also axially movable relative to the first end portion 16.

[0012] The pylon 14 of FIG. 1 is shown in more detail in FIG. 2. The first end portion 16 includes a conventional attachment plate 24 which attaches to the conventional socket (not shown in FIG. 2) in a well known manner. The angle of the attachment plate 24 may be adjusted with adjustment bolts 26.

[0013] The first end portion 16 also includes a piston chamber 28 receiving a piston 30. The piston chamber 28 is preferably made of aluminum or titanium, and the piston 30 is preferably made of titanium.

[0014] The piston 30 has an O-ring seal 32 mounted in a groove about its circumference so that the piston chamber 28 contains an enclosed, sealed area 34. Alternatively, the piston chamber 28 can be enclosed and sealed by a membrane 32 a (FIG. 4) attached to the inner walls of the piston chamber 28 and positioned orthogonally to the longitudinal axis 22. As another alternative, the piston chamber 28 can include a fluid bladder 32 b (FIG. 5) which is enclosed and sealed.

[0015] A retainer block 36 retains the piston 30 in the piston chamber 28, and O-ring bumpers 40 cushion the impact of the piston 30 against the retainer block 36. A bearing, such as a wear ring 44, is mounted about the circumference of the piston 30 in contact with the inner walls of the piston chamber 28, and a bearing, such as a wear ring 48, is mounted in the retainer block 36 in contact with the piston 30. The wear rings 44 and 48 are preferably made of TURCITE-X®, and will be discussed in more detail below.

[0016] The pylon 14 also has a torsional spring including cushions (not shown in FIG. 2) and a torsion key 52 rotatably mounted at one end in a bearing 54 seated in an interior end of the piston chamber 28. The cushions and the torsion key 52 are retained by a stop plate 56. A slot in the head of the piston 30 receives the other end of the torsion key 52 in a torsion slide 58 preferably made of TURCITE-X®. As a result, the torsion key 52 slides into and out of the head of the piston 30 with little resistance, but it is forced to rotate in its bearing 54 against the cushions (not shown in FIG. 2) about the longitudinal axis 22 when the piston 30 rotates relative to the piston chamber 28. The torsion key 52 and cushions will be described in more detail below.

[0017] In operation, the area 34 contains a compressible volume of fluid, preferably air. However, the fluid can also be, for example, another compressible gas or an incompressible liquid containing compressible objects 25. Those having skill in the field of this invention will understand that a wide variety of compressible volumes of fluid fall within the scope of this invention. Also, it is preferable that the pylon 14 include a fitting 60 so that the compressible volume of fluid can be pressurized. This allows a patient to customize the response of the pylon 14.

[0018] As the patient moves forward, the heel of the prosthetic foot (not shown in FIG. 2) strikes the ground. At this time, a force F_(w) due to the patient's weight is impressed on the piston 30, and the piston 30 slides into the piston chamber 28 resisted by a pressure force F_(p) as the compressible volume of fluid compresses. As a result, substantially all of the patient's weight applied to the piston 30 is resiliently cushioned by the compressible volume of fluid. At the same time, the torsion key 52 slides into the slot in the head of the piston 30.

[0019] As the patient continues forward, the patient's weight is transferred from the heel to a point forward on the prosthetic foot (not shown in FIG. 2) impressing a moment on the piston 30 relative to the piston chamber 28 which may, for example, be resolved into a couple including a moment M_(w) centered on the wear ring 48 and a force F_(a), imposed on the wear ring 48. This moment M_(w) impresses a force F_(b) on the wear ring 44, for example, as follows:

Fb=(M _(w) /d _(b))  (1)

[0020] where d_(b) is the length of the moment arm at the wear ring 44. Because of the coefficients of friction μ_(a), μ_(b) between the wear rings 48 and 44 and the piston 30 and the inner wall of the piston chamber 28, respectively, the forces F_(a) and F_(b) cause the wear rings 44 and 48 to resist motion by the piston 30 with a friction force F_(F) equal to:

F _(F)=(μ_(a) F _(a)+μ_(b) F _(b))  (2)

[0021] At a point during the patient's movement forward when the toes of the prosthetic foot (not shown in FIG. 2) are on the ground and the heel is beginning to rise, the moment M_(w) and the force F_(a) reach their maximum. At this point in the patient's gait, the pressure force F_(p) tries to urge the piston 30 out of the piston chamber 28, but the friction force F_(F) (which is at its maximum because of the maximized moment M_(w) and force F_(a)) advantageously restricts motion by the piston 30.

[0022] When the moment M_(w) and the force F_(a) decrease from their maximum values as the patient continues forward, and the force F_(w) due to the patient's weight lessens as the patient's weight shifts to the other leg, the friction force F_(F) decreases sufficiently to allow the pressure force F_(p) to rapidly urge the piston 30 out of the piston chamber 28. As a result the patient receives an advantageous boost forward. The timing and amount of the boost can, of course, be controlled by varying the pressurization of the compressible volume of fluid through the fitting 60, by varying the length of the moment arm d_(b), and by varying the coefficients of friction μ_(a) and μ_(b).

[0023] The torsion key 52 is shown in more detail in FIG. 3. It includes projections 52 a and 52 b which compress cushions 64 a, 64 b, 64 c, 64 d when the torsion key 52 is rotated by the piston (not shown in FIG. 3) about the longitudinal axis 22 of the pylon (not shown in FIG. 3). In this manner, the torsion key 52 resists rotation by the piston, and hence by the patient's leg stump (not shown in FIG. 3), about the longitudinal axis 22. The cushions 64 a, 64 b, 64 c, 64 d are preferably made of polyurethane, and they allow a range of rotation by the torsion key 52 of approximately ±15°.

[0024] In an alternative embodiment, the shapes, positions and spring rates of the cushions 64 a, 64 b, 64 c, 64 d may be selected so that the cushions 64 a, 64 b, 64 c, 64 d resist clockwise rotation by the torsion key 52 with a different force than they resist counter-clockwise rotation. It may, for example, be advantageous to have a different resistance to clockwise and counter-clockwise rotation according to whether the pylon (not shown in FIG. 3) is attached to a right or a left leg stump. Also, it will be understood that a wide variety of alternative configurations for the cushions are possible—including more or less than four cushions—and that these alternative configurations fall within the scope of the present invention.

[0025] The present invention thus advantageously provides a pylon which is cushioned and resilient. It also provides a patient a boost forward at an advantageous moment in their stride.

[0026] Although the present invention has been described with reference to a preferred embodiment, the invention is not limited to this preferred embodiment. Rather, the invention is limited only by the appended claims, which include within their scope all equivalent devices or methods which operate according to the principles of the invention as described. 

We claim:
 1. A pylon for supporting the weight of a patient with a leg stump on a prosthetic foot supported by the ground, the pylon comprising: a first end portion connectable to one of the leg stump and a prosthetic knee; a second end portion opposing the first end portion and connectable to one of a prosthetic knee and a prosthetic foot, the second end portion being axially movable relative to the first end portion along a longitudinal axis of the pylon; an enclosed compressible volume of fluid between the first and second end portions and through which a substantial portion of the patient's weight applied through the patient's leg stump to the first end portion is supportable; and a rotational stabilizer between the first and second end portions for resisting relative rotation between the first and second end portions without supporting a substantial portion of the patient's weight applied through the patient's leg stump to the first end portion, at least a portion of the rotational stabilizer being positioned within the enclosed compressible volume of fluid.
 2. The pylon of claim 1, wherein the rotational stabilizer is substantially oval in cross-sectional shape.
 3. The pylon of claim 1, wherein the compressible volume of fluid is a volume of air.
 4. The pylon of claim 1, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible volume of fluid is enclosed by the piston head and the piston chamber.
 5. The pylon of claim 4, wherein the piston has a seal circumferentially mounted thereon so that the piston head and piston seal together seal the portion of the piston chamber containing the compressible volume of fluid.
 6. The pylon of claim 1, wherein the compressible volume of fluid is enclosed and sealed so that it can be pressurized.
 7. A pylon for supporting the weight of a patient with a leg stump on a prosthetic foot supported by the ground, the pylon comprising: a first end portion connectable to one of the leg stump and a prosthetic knee; a second end portion opposing the first end portion and connectable to one of a prosthetic knee and a prosthetic foot, the second end portion being axially movable relative to the first end portion along a longitudinal axis of the pylon; a compressible medium between the first and second end portions and positioned along the longitudinal axis of the pylon so that a substantial portion of the patient's weight applied through the patient's leg stump to the first end portion is supportable through the compressible medium, wherein the compressible medium is compressed during heel strike of the prosthetic foot and is decompressed when the patient's weight shifts during movement of the prosthetic foot; and a bearing between the first and second end portions that allows the first end portion to slide with respect to the second end portion.
 8. The pylon of claim 7, wherein: one of the first and second end portions is connected to a piston; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the bearing is positioned between the piston and an interior wall of the piston chamber.
 9. The pylon of claim 7, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible medium is enclosed by the piston head and the piston chamber.
 10. The pylon of claim 9, wherein the piston has a seal circumferentially mounted thereon so that the piston head and piston seal together seal the portion of the piston chamber containing the compressible medium.
 11. The pylon of claim 7, wherein the compressible medium is enclosed and sealed so that it can be pressurized.
 12. The pylon of claim 7, wherein at least a portion of the rotational stabilizer is positioned within the compressible medium.
 13. A method of supporting the weight of a patient having a leg stump on a prosthetic foot supported by the ground, the method comprising: supporting the patient's leg stump on the prosthetic foot through an enclosed compressible volume of fluid connected to a pylon so that a substantial portion of the patient's weight supported on the prosthetic foot is supported by the enclosed compressible volume of fluid; compressing the enclosed compressible volume of fluid during heel strike of the prosthetic foot; decompressing the enclosed compressible volume of fluid when the patient's weight shifts during movement of the prosthetic foot; and resisting rotation of the patient's leg stump relative to the prosthetic foot about a longitudinal axis of the pylon without inducing axial forces between the leg stump and the prosthetic foot.
 14. The method of claim 13, and further comprising adjusting a pressure of the enclosed compressible volume of fluid to customize the pylon according to the patient's needs.
 15. A pylon for supporting the weight of a patient with a leg stump on a prosthetic foot supported by the ground, the pylon comprising: a first end portion connectable to one of the leg stump and a prosthetic knee; a second end portion opposing the first end portion and connectable to one of a prosthetic knee and a prosthetic foot, the second end portion being axially movable relative to the first end portion along a longitudinal axis of the pylon; an enclosed compressible volume of fluid between the first and second end portions, the compressible volume of fluid supporting and cushioning axial loads along the longitudinal axis of the pylon; and a rotational stabilizer coupled to the first and second end portions, the rotational stabilizer resisting relative rotation between the first and second end portions and allowing substantially unrestricted axial movement between the first and second end portions.
 16. The pylon of claim 15, wherein the rotational stabilizer is substantially oval in cross-sectional shape.
 17. The pylon of claim 15, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible volume of fluid is enclosed by the piston head and the piston chamber.
 18. The pylon of claim 17, wherein the piston has a seal circumferentially mounted thereon so that the piston head and piston seal together seal the portion of the piston chamber containing the compressible volume of fluid.
 19. The pylon of claim 15, wherein the compressible volume of fluid is enclosed and sealed so that it can be pressurized.
 20. The pylon of claim 15, wherein at least a portion of the rotational stabilizer is positioned within the compressible volume of fluid.
 21. A pylon for a lower limb prosthetic assembly attachable to a patient, the pylon comprising: a first member connectable to one of the leg stump and a prosthetic knee; a second member connected to the first member and connectable to one of a prosthetic knee and a prosthetic foot, the first and second members being axially movable with respect to each other along the longitudinal axis of the pylon; a compressible medium between the first and second members, the compressible medium supporting a substantial portion of an axially compressive load along the longitudinal axis of the pylon applied by the patient; and a rotational stabilizer between the first and second members, the rotational stabilizer having a first element connected to at least one of the first and second members to allow substantially unrestricted axial movement therebetween, and the rotational stabilizer having a second element connected to at least one of the first and second members to oppose rotation between the first and second members.
 22. The pylon of claim 21, wherein: one of the first and second members is connected to a piston having a head; the other of the first and second members is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible medium is enclosed by the piston head and the piston chamber.
 23. A pylon for a lower limb prosthesis assembly attachable to a patient, the pylon comprising: a first member connectable to one of a leg socket or a prosthetic foot; a second member connectable to the other of the leg socket or the prosthetic foot and connected to the first member, the first and second members being axially movable with respect to each other along the longitudinal axis of the pylon; an enclosed compressible volume of fluid between the first and second members, the compressible volume of fluid supporting a substantial portion of an axially compressive load along the longitudinal axis of the pylon applied by the patient; a fitting attached to a chamber enclosing the compressible volume of fluid for adjustably pressurizing the compressible volume of fluid; and a rotational stabilizer between the first and second members, the rotational stabilizer having a first portion connected to at least one of the first and second members to allow substantially unrestricted axial movement therebetween, and the rotational stabilizer having a second portion connected to at least one of the first and second members to oppose rotation between the first and second members.
 24. The pylon of claim 23, wherein the rotational stabilizer is substantially oval in cross-sectional shape.
 25. The pylon of claim 23, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible volume of fluid is enclosed by the piston head and the piston chamber.
 26. The pylon of claim 25, wherein the piston has a seal circumferentially mounted thereon so that the piston head and piston seal together seal the portion of the piston chamber containing the compressible volume of fluid.
 27. The pylon of claim 23, wherein the compressible volume of fluid is enclosed and sealed so that it can be pressurized.
 28. The pylon of claim 23, wherein at least a portion of the rotational stabilizer is enclosed within the compressible volume of fluid.
 29. A method of supporting the weight of a patient having a leg stump on a prosthetic foot supported by the ground the method comprising: supporting the patient's leg stump on the prosthetic foot through a compressible medium connected to a pylon so that a substantial portion of the patient's weight supported on the prosthetic foot is supported by the compressible medium; compressing the compressible medium during heel strike of the prosthetic foot; decompressing the compressible medium when the patient's weight shifts during movement of the prosthetic foot; adjusting the compressible medium to customize the pylon according to the patient's needs; and resisting rotation of the patient's leg stump relative to the prosthetic foot about a longitudinal axis of the pylon.
 30. A pylon for supporting the weight of a patient with a leg stump on a prosthetic foot supported by the ground, the pylon comprising: a first end portion connectable to one of the leg stump and a prosthetic knee; a second end portion opposing the first end portion and connectable to one of a prosthetic knee and a prosthetic foot, the second end portion being rotatable and axially movable relative to the first end portion about and along a longitudinal axis of the pylon, respectively; a compressible medium between the first and second end portions, the compressible medium supporting and cushioning axial loads along the longitudinal axis of the pylon; and a torsional spring connected to at least one of the first and second end portions, the torsional spring resisting relative rotation between the first and second end portions to bias at least one of the first and second end portions to a predetermined position, and the torsional spring allowing substantially unrestricted axial movement between the first and second end portions.
 31. The pylon of claim 30, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible medium is positioned between the piston head and the piston chamber.
 32. The pylon of claim 30, wherein the torsional spring resists clockwise rotation with a first resistive rate and counter-clockwise rotation with a second resistive rate different from the first resistive rate.
 33. A pylon for supporting the weight of a patient with a leg stump on a prosthetic foot supported by the ground, the pylon comprising: a first end portion connectable to one of the leg stump and a prosthetic knee; a second end portion opposing the first end portion and connectable to one of a prosthetic knee and a prosthetic foot, the second end portion being rotatable and axially movable relative to the first end portion about and along a longitudinal axis of the pylon, respectively; a compressible medium between the first and second end portions, the compressible medium supporting and cushioning axial loads along the longitudinal axis of the pylon; a fitting attached to a chamber enclosing the compressible medium for adjustably pressurizing the chamber; and a rotational stabilizer connected to at least one of the first and second end portions, the rotational stabilizer resisting relative rotation between the first and second end portions to bias at least one of the first and second end portions to a predetermined position.
 34. The pylon of claim 33, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible medium is enclosed by the piston head and the piston chamber.
 35. The pylon of claim 33, wherein at least a portion of the compressible medium is a compressible volume of fluid that is enclosed and sealed so that it can be pressurized.
 36. A pylon for supporting the weight of a patient with a leg stump on a prosthetic foot supported by the ground, the pylon comprising: a first end portion connectable to one of the leg stump and a prosthetic knee; a second end portion opposing the first end portion and connectable to one of a prosthetic knee and a prosthetic foot, the second end portion being rotatable and axially movable relative to the first end portion about and along a longitudinal axis of the pylon, respectively; a compressible medium between the first and second end portions and positioned along the longitudinal axis of the pylon so that a substantial portion of the patient's weight applied through the patient's leg stump to the first end portion is supportable through the compressible medium; and a rotational stabilizer connected to at least one of the first and second end portions for resisting relative rotation between the first and second end portions, the rotational stabilizer resisting clockwise rotation with a first resistive rate and counter-clockwise rotation with a second resistive rate different from the first resistive rate.
 37. The pylon of claim 36, wherein: one of the first and second end portions is connected to a piston having a head; the other of the first and second end portions is connected to a piston chamber for receiving the piston along the longitudinal axis of the pylon; and the compressible medium is positioned between the piston head and the piston chamber. 